1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) apparatus for displaying colors according to applied voltages, and a method of driving the same.
This invention also relates to a power supply circuit suitable for an LCD apparatus which displays colors according to applied voltages, and, more particularly, to an LCD apparatus which can easily execute the fine adjustment of display colors and a power supply circuit for this LCD apparatus.
2. Description of the Related Art
Color display apparatuses provide arbitrary display colors by combining primary colors of red, green and blue, and have dots corresponding to those primary colors. This type of color display apparatus displays arbitrary colors by independently controlling the brightness of the red, green and blue dots corresponding to the individual primary colors. Therefore, a television set, personal computer or the like, which is equipped with such a color display apparatus, supplies three pieces of luminance data corresponding to the primary colors of red, green and blue to the display apparatus and controls the brightness of the individual color dots in accordance with those luminance data of the primary colors, thereby displaying the desired color pixel by pixel.
In a color LCD device, likewise, electrodes forming a plurality of dots are arranged in such a manner that three dots corresponding to the color filters of the primary colors (red, green and blue) form a single pixel, and the intensities of light passing those dots are independently controlled to select the display color for each pixel formed by the three dots.
Since an LCD apparatus equipped with such color filters has a low light transmittivity, a transparent type which has a strong light source located at the back of the apparatus is employed in a television set, a personal computer, etc.
Because the aforementioned color LCD device suffers large light absorption by the color filters, however, a color LCD apparatus of a reflection type which utilizes the reflection of outside light cannot be provided.
An electrically controlled birefringence (ECB) type LCD device is known which can display a color image without using a color filter. The ECB type LCD device comprises a liquid crystal (LC) cell where liquid crystal is sealed, and two polarization plates arranged so as to sandwich the LC cell. The ECB type LCD device alters the molecular alignment of the liquid crystal by an applied electric field. When the molecular alignment changes, the birefringence of the LC layer changes and the polarization state of light passing the LC cell varies. Accordingly, the spectrum distribution of the light leaving the polarization plate on the outgoing side varies, displaying the desired color.
Since the ECB type LCD device does not cause light absorption by color filters, the display is bright. The ECB type LCD device can therefore be used as a reflection type color LCD device, and is still advantageous in its simple structure.
The ECB type LCD device provides display colors each in one-to-one association with the voltage applied between the electrodes constituting a single pixel. It is not therefore possible to activate and drive the ECB type LCD device with luminance data corresponding to the primary colors of red, green and blue supplied to the conventional color display apparatus like a CRT.
But, the number of colors that the conventional ECB type LCD device can display is limited to the number of applied voltages. As the displayed colors pass a predetermined locus on a chromaticity diagram with respect to a change in applied voltage, the number of display colors is limited. It is therefore difficult to obtain arbitrary display colors corresponding to the supplied luminance data of red, green and blue.
The number of voltages applicable to the ECB type LCD device from the driving circuit is limited. Each display color shows a sharp change and a gentle change in accordance with a change in applied voltage. The distance between displayable colors may become very large. To avoid this problem, it is necessary to increase the number of applicable voltages. Increasing the number of applicable voltages, however, complicates the circuit structure and adjustment of a power supply section and increases the manufacturing cost.